1. Field of the Invention
The present invention relates to navigation apparatuses. More specifically, the present invention relates to a navigation apparatus that has a route searching function for searching for a route to a destination, a detour route searching function for searching for a detour route for detouring around a partial segment of a route found by the route searching function, and a return route searching function for searching for a return route for returning to an original route when a vehicle turns off the route.
2. Description of the Related Art
On-vehicle navigation apparatuses generally have various functions including a map displaying function for displaying a map of the vicinity of the position of the vehicle on a screen, a route searching function for searching for a route to a destination or a point on route specified by a user, and a route guidance function for guiding the vehicle to travel along a route found by a route search.
Furthermore, many navigation apparatuses have a detour route searching function for searching for a detour route for detouring around a segment of a current route, for example, when the traffic is heavy on the current route, and a return route searching function for searching for a return route for returning to an original route when the vehicle turns off the route.
For the detour route searching function, a distance to be detoured (e.g., two kilometers) is specified and a high cost is set for a road in the segment to be detoured, so that a detour route for returning to an initial route is searched for while avoiding the segment.
For the return route searching function, when the vehicle turns off the route, a route for returning to a point on an initial route (e.g., an intersection that has not been passed and that is nearest to the position of the vehicle) at an optimal cost is searched for as a return route.
In a conventional navigation apparatus, it sometimes occurs that an inappropriate detour route is set when a search for a detour route is repeated in a relatively short period.
FIGS. 10A to 10C are diagrams showing an example where an inappropriate detour route is set in a conventional navigation apparatus. A case where a route r1 to a destination d is set and an instruction for calculation of a detour route is issued three times repeatedly, as shown in FIG. 10A, will be considered. Since it is unlikely that a user changes the detour distance each time the calculation instruction is issued, it is assumed that the detour distance is fixed at a preset value (e.g., two kilometers).
In this case, when a first instruction for calculation of a detour route is issued, a detour route r2 for returning to the initial route r1 from the current position g of the vehicle while detouring a segment p1 corresponding to the detour distance is searched for, as shown in FIG. 10A. Then, when a second instruction for calculation of a detour route is issued, a new return route r3 for returning to the previous detour route r2 from the current position g of the vehicle while detouring a segment p2 corresponding to the detour distance is searched for, as shown in FIG. 10B. Then, when a third instruction for calculation of a detour route is issued, a new return route r4 for returning to the previous detour route r3 from the current position g of the vehicle while detouring a segment p3 corresponding to the detour distance is searched for, as shown in FIG. 10C.
When a search for a detour route is repeated in a relatively short period as described above, in order to return to the original route r1, the vehicle first returns to the detour route r3 via the detour route r4, then returns to the detour route r2 via the detour route r3, and finally returns to the original route r1 via the detour route r2, as shown in FIG. 10C. Thus, more than a necessary number of right turns and left turns are made to return to the original route r1; that is, a detour route with many deviations overall is set. Such a return route incurs an increased travel distance and time, which is inappropriate in consideration of the original intent to find a detour route for detouring part of the original route r1 in order to avoid an increase in travel time due to heavy traffic, etc. That is, the conventional navigation apparatus suffers from a problem that an inappropriate route is set when a search for a detour route is repeated several times.
Furthermore, when a search for a detour route has been repeated several times, in some cases more reasonable route guidance can be achieved by newly searching at that time for a route directly going to the destination than by returning to the original route. However, the conventional navigation apparatus does not execute such a process, and it simply searches for a detour route for returning to the original route irrespective of the current position of the vehicle, the distance to the destination, the distance of the detour route, etc.
A similar problem may also arise in searching for a return route when the vehicle has turned off a guided route. For example, when the vehicle has turned off an original route, a return route for returning to the original route is searched for, and if the vehicle further turns off the return route repeatedly, in some cases more reasonable route guidance can be achieved by newly searching at that time for a route directly going to the destination than by searching for a new return route for returning to the previous return route (or to the original route) each time. Even in such cases, the conventional navigation apparatus does not execute such a process, and it sometimes sets a lengthy, inappropriate return route irrespective of the current position of the vehicle, the distance to the destination, the distance of the detour route, etc., similar to the case of the detour route described above.
The present invention has been made in view of the above problems, and it is an object of the present invention to provide a navigation apparatus in which the selection of an inappropriate route is prevented when a detour route or return route is calculated.
To this end, the present invention, in one aspect thereof, provides a navigation apparatus including a destination setting device for setting a destination; a route searching device for searching for an initial route to the destination set by the destination setting device, under a given condition; a detour calculation instruction device for instructing the calculation of a detour route; and a detour route searching device for searching for a detour route for returning to the initial route, wherein when an instruction for first calculation of a detour route is issued by the detour calculation instruction device with a detour distance specified, the detour route searching device searches for a detour route while increasing the cost of a link corresponding to the detour distance specified by the detour calculation instruction device, whereas when an instruction for a second or subsequent calculation of a detour route is issued, the detour route searching device searches for a detour route while increasing the cost of each link corresponding to a detour route that has been found according to a previous instruction for the calculation of a detour route.
When a second or subsequent calculation of a detour route is instructed, the cost of a link corresponding to the entire previous detour route is increased before searching for a new detour route for returning to the initial route, so that the selection of a lengthy, inappropriate detour route is prevented even if the search for a detour route is executed a plurality of times.
Preferably, the navigation apparatus further includes a route researching device for searching again for a route to the destination set by the destination setting device when an instruction for a second or subsequent calculation of a detour route is issued and if a ratio of a distance of a detour route found by the detour route searching device exceeds a preset value. If the ratio of a detour route exceeds the preset value, that is, if the detour route is too long, a route from the current position of the vehicle to the destination is searched for again instead of searching for a detour route for returning to the initial route, so that an appropriate route with a short traveling distance, traveling time, etc. is found.
Preferably, the navigation apparatus further includes an instruction screen display device for displaying an instruction screen, the instruction screen including a first area for selecting one of a plurality of candidates of detour distance and for instructing the calculation of a detour route, and a second area for instructing the calculation of a detour route without specifying a detour distance, wherein, when the second area included in the instruction screen is specified by the detour calculation instruction device, the detour route searching device searches for a detour route assuming that a second or subsequent calculation of a detour route has been instructed. Since the first area for showing a plurality of candidates of detour distance and for selecting one therefrom is provided, ease of operation in specifying a detour distance is improved. Furthermore, since the second area for instructing the calculation of a detour route without specifying a detour distance is provided, the operation for instructing a second or subsequent search for a detour route is facilitated.
Preferably, the instruction screen display device prohibits the selection of a candidate of detour distance, included in the first area, that has already been selected in a state where an instruction for a second or subsequent calculation of a detour route is allowed. Because the same detour distance is prohibited from being selected more than once, the selection of a lengthy detour route resulting from repeating the same detour distance a plurality of times is prevented.
Preferably, the navigation apparatus further includes a vehicle position detecting device for detecting a current position of a vehicle, wherein, when a second or subsequent calculation of a detour route is instructed, the detour route searching device sequentially tracks each detour route that has been found according to a previous instruction for calculation of a detour route from the current position of the vehicle to the initial route before executing a search for a detour route according to the instruction for a second or subsequent calculation of a detour route, and increases the cost of each link that constitutes each detour route that has been tracked. Accordingly, a new detour route is found while avoiding as much as possible a detour route that has previously been found.
Preferably, the detour route searching device increases the cost of each link by multiplying the original cost thereof by a multiplier value, the multiplier value increasing in order of a detour route including the link being a minor street, a main road, and a highway. Accordingly, minor streets, main roads, and highways are selected in that order of priority when searching for a detour route, so that an efficient detour route is calculated.
Preferably, the ratio is the ratio of a distance of a previous detour route found by a previous search for a detour route by the detour route searching device to a total distance to be traveled when the vehicle returns to the initial route via the previous detour route and travels to the destination. Accordingly, it is determined what percentage of the entire route to be traveled when the vehicle returns to the initial route via the detour route and travels to the destination is represented by the detour route, so that whether the detour route too long can be accurately evaluated.
Alternatively, the ratio may be a ratio of the distance of a previous detour route to a total distance to be traveled when the vehicle travels from the current position to the destination along the initial route. Accordingly, it is determined what percentage of the total distance to be traveled when the vehicle travels from the current position to the destination via the initial route is represented by the detour route, so that whether the detour route too long can be accurately evaluated.
Yet alternatively, the ratio may be a ratio of the distance of a previous detour route to a straight line distance from the current position of the vehicle to the destination. By calculating the ratio as such, whether the detour route is too long can be approximately evaluated. This method in particular is advantageous because the calculation is simple and processing is simplified.
Preferably, the ratio is set to be 25%. Most users will feel that detour routes with a distance ratio exceeding approximately 1/4 to be too long. Accordingly, evaluation will be in accordance with the user""s taste by using the ratio of 25% as a criterion.
The navigation apparatus may further include a ratio setting device for arbitrarily setting the ratio within a predetermined range. Accordingly, for example, when an individual user feels that a default value of the ratio is inappropriate, the user is allowed to change the value of the ratio as desired.
The present invention, in another aspect thereof, provides a navigation apparatus including a vehicle position detecting device for detecting the current position of a vehicle; a destination setting device for setting a destination; a route searching device for searching for an initial route to the destination set by the destination setting device, under a given condition; a recalculation instruction device for determining whether the current position of the vehicle detected by the vehicle position detecting device is off the initial route found by the route searching device, and for instructing the recalculation of a route if the current position of the vehicle is determined to be off the initial route; and a return route searching device for searching for a return route; wherein, when a first recalculation is instructed by the recalculation instruction device, the return route searching device searches for a return route for returning to the initial route found by the route searching device, whereas when a second or subsequent recalculation is instructed, the return route searching device searches again for a route to the destination if the ratio of a return route that has previously been found exceeds a preset value while searching for a different return route for returning to the initial route if the ratio does not exceed the preset value.
When a second or subsequent recalculation is instructed and if the ratio of a previous route that has previously been found exceeds the preset value, that is, if the return route is too long, an appropriate route with a shorter travel distance and time is often found by searching again for a route from the current position of the vehicle to the destination instead of searching for a return route for returning to the initial route. Accordingly, if the ratio of the previously found return route exceeds the preset value, a route to the destination is searched for again, so that the selection of a lengthy, inappropriate return route is prevented.
Preferably, the return route searching device searches for a different return route for returning to the initial route until a recalculation is instructed more than a predetermined number of times by the recalculation instruction device. Until a recalculation is instructed more than the predetermined number of times, it can be assumed that the current position of the vehicle is not so far off the initial route and that a return route not so lengthy will usually be found. Accordingly, in such a case, a different return route is searched for, so that processing load is reduced and route guidance is resumed more quickly compared with a case where an entire route to the destination is searched for again.
Preferably, the ratio is a ratio of the distance of a previous return route found by a previous search for a return route by the return route searching device to a total distance to be traveled when the vehicle returns to the initial route via the previous return route and travels to the destination. Accordingly, it is determined what percentage of the entire route to be traveled when the vehicle returns to the initial route via the return route and travels to the destination is represented by the return route, so that whether the return route is lengthy can be accurately evaluated.
Alternatively, the ratio may be a ratio of the distance of a previous return route to a total distance to be traveled when the vehicle travels from a current position to the destination along the initial route. Accordingly, it is determined what percentage of the total distance to be traveled when the vehicle travels from the current position to the destination via the initial route is represented by the return route, so that whether the return route is lengthy can be accurately evaluated.
Yet alternatively, the ratio may be the ratio of the distance of a previous return route to a straight line distance from a current position of the vehicle to the destination. By calculating the ratio as such, whether the return route is too long can be approximately evaluated. This method in particular is advantageous because the calculation is simple and processing is simplified.
Preferably, the navigation apparatus further includes a ratio setting device for arbitrarily setting the ratio within a predetermined range. Accordingly, for example, when an individual user feels that a default value of the ratio is inappropriate, the user is allowed to change the value of the ratio as desired.